Check format and dimensions
Many portals require specific formats such as JPEG, PNG, or WebP. Others set minimum and maximum dimensions.
Resize first, then compress. Compressing a huge original without resizing can still leave a file larger than the upload limit.
Use clear filenames
Camera filenames do not describe the content. Rename images with a short purpose, date, or subject before sending.
Avoid private names, customer details, and internal project labels in public image filenames.
Review the final preview
After upload, check how the image appears inside the actual page or form. A file can be technically accepted but still cropped badly.
If the portal creates thumbnails, inspect those too. Small previews can make fine text or labels unreadable.